This invention relates to radio frequency receivers and processing techniques and more particularly to an improved superheterodyne receiver and method.
In a superheterodyne receiver, the process of mixing the output of an LO with an RF signal produces frequency components that fall within the IF band if the signal is either higher in frequency than the LO by the IF, called "top side" down conversion, or lower in frequency than the LO, called "low side" down conversion. Thus, the IF represents frequencies that are converted either from the "top side" of the LO or the "low side" of the LO.
In order to reject or suppress the image IF signal in accordance with conventional practice, an RF preselector filter or the like is used on the input side of the mixer to prevent signals from the RF band on either the high or low sides of the LO from being processed in the receiving system. While this eliminates the image IF, there is a substantial loss of the receiving bandwidth capability for the system, i.e., one-half of the potential receiving capability. In addition, the preselection filters are somewhat costly.
This invention is directed to a solution of these problems.